ZLACN2(1) LAPACK auxiliary routine (version 3.2) ZLACN2(1)NAMEZLACN2 - estimates the 1-norm of a square, complex matrix A
SYNOPSIS
SUBROUTINE ZLACN2( N, V, X, EST, KASE, ISAVE )
INTEGER KASE, N
DOUBLE PRECISION EST
INTEGER ISAVE( 3 )
COMPLEX*16 V( * ), X( * )
PURPOSEZLACN2 estimates the 1-norm of a square, complex matrix A. Reverse
communication is used for evaluating matrix-vector products.
ARGUMENTS
N (input) INTEGER
The order of the matrix. N >= 1.
V (workspace) COMPLEX*16 array, dimension (N)
On the final return, V = A*W, where EST = norm(V)/norm(W) (W
is not returned).
X (input/output) COMPLEX*16 array, dimension (N)
On an intermediate return, X should be overwritten by A * X,
if KASE=1, A' * X, if KASE=2, where A' is the conjugate trans‐
pose of A, and ZLACN2 must be re-called with all the other
parameters unchanged.
EST (input/output) DOUBLE PRECISION
On entry with KASE = 1 or 2 and ISAVE(1) = 3, EST should be
unchanged from the previous call to ZLACN2. On exit, EST is an
estimate (a lower bound) for norm(A).
KASE (input/output) INTEGER
On the initial call to ZLACN2, KASE should be 0. On an interme‐
diate return, KASE will be 1 or 2, indicating whether X should
be overwritten by A * X or A' * X. On the final return from
ZLACN2, KASE will again be 0.
ISAVE (input/output) INTEGER array, dimension (3)
ISAVE is used to save variables between calls to ZLACN2FURTHER DETAILS
Contributed by Nick Higham, University of Manchester.
Originally named CONEST, dated March 16, 1988.
Reference: N.J. Higham, "FORTRAN codes for estimating the one-norm of a
real or complex matrix, with applications to condition estimation", ACM
Trans. Math. Soft., vol. 14, no. 4, pp. 381-396, December 1988. Last
modified: April, 1999
This is a thread safe version of ZLACON, which uses the array ISAVE in
place of a SAVE statement, as follows:
ZLACON ZLACN2
JUMP ISAVE(1)
J ISAVE(2)
ITER ISAVE(3)
LAPACK auxiliary routine (versioNovember 2008 ZLACN2(1)